Looking for decentralized communication?

Email http://en.wikipedia.org/wiki/Bitmessage

http://en.wikipedia.org/wiki/Freenet
Offers Email via Freemail plugin and...
https://wiki.freenetproject.org/Sone
http://jtcfrost.sourceforge.net/

Micro-blogging http://en.wikipedia.org/wiki/Twister_(software)
https://twisterio.com/

Forums?  Never used, but sounds promising.
http://getaether.net/